A technology for configuring a RAID (Redundant Array of Independent Disks) and preventing the loss of data in accordance with a storage system controller controlling multiple storage devices is known. For example, in a storage system, which uses RAID 5, the storage system controller, which is equivalent to a higher-level apparatus with respect to the storage device, creates parity from multiple data blocks.
There is a storage system in which the respective storage devices, which are equivalent to lower-level apparatuses, configure a RAID in order to reduce the processing of the storage system controller pursuant to creating the parity mentioned hereinabove. Each storage device, for example, is a HDD (Hard Disk Drive), and the controller of each HDD (hereinafter, HDD controller) creates parity.
For example, in Patent Literature 1, when there is a data update request with respect to pre-update data (old data), the HDD controller updates the old data to new data after creating an intermediate value (intermediate parity) for creating parity from the updated data (new data) and the pre-update data (old data). The HDD controller transfers the created intermediate parity to the HDD in which an old parity corresponding to the old data is being stored. In the HDD, which receives the intermediate parity, the HDD controller creates new parity from the intermediate parity and the old parity, and updates the old data with the created new parity.
In line with the lowering of flash memory prices in recent years, Flash SSD (Flash Solid State Drive) has been increasingly used in place of HDD as a storage device. In the HDD, when there is an update request with respect to data identified by a certain range of logical addresses, updated data (new data) is overwritten to the physical area in which the relevant data (old data) is stored. However, in the Flash SSD, since the overwriting of data is not possible, when there is an update request for data identified by a logical address, the updated data is stored in a physical area, which differs from the physical area in which the relevant data is stored, and the new physical area is mapped to the identified logical address. In accordance with this, the physical area in which the old data is stored in the Flash SSD is made invalid.